This invention relates generally to methods, instrumentation and devices for humeral implant positioning and more particularly to an improved trialing system utilizing an adjustment instrument and orientation indicia.
The shoulder is one of the most complex joints in the body. Proper treatment of shoulder disorders and conditions involves solving many complex issues to achieve optimal clinical results. During a shoulder replacement operation, at least a portion of the proximal section of the humeral shaft will be replaced by a metal prosthesis. This prosthesis will generally consist of two parts: a stem that is mounted into the medullary canal of the humerus and a head component connected in some manner to the stem. The head component replaces the bearing surface of the humerus and articulates with the surface of the glenoid to allow the movement of the shoulder.
The stem and head components of a humeral prosthesis may be supplied in xe2x80x9cmodularxe2x80x9d form, that is, as separate connectable components. Different stem sizes and head sizes in a modular implant design provide the surgeon with some degree of flexibility, which facilitates reconstruction of the original anatomy of the patient.
With a range of stem sizes and a range of head sizes available, the surgeon can choose a particular combination to suit the anatomy of each individual patient without having a large inventory of xe2x80x9cintegralxe2x80x9d or xe2x80x9cunitaryxe2x80x9d humeral prostheses. As used herein, xe2x80x9cintegralxe2x80x9d and xe2x80x9cunitaryxe2x80x9d mean formed in one continuous piece in contrast to the separate connectable components of a modular prosthesis. For example, one patient may require a relatively small head and a relatively long stem. With a unitary prosthesis, a wide range of stem lengths and diameters are required for each head size, whereas with a modular arrangement, a particular head may be used with a range of stem sizes, and a particular stem may be used with a variety of head sizes.
Additional variations also arise because individual patients may require differing angles of inclination of the head relative to the stem and differing eccentricities between the axis of the head and the axis of the stem. Thus, for example, in one patient, the eccentricity may be posterior and in another patient, it may be anterior. A modular shoulder prosthesis is disclosed in U.S. Pat. No. 6,197,063 B1, the entirety of which is hereby incorporated by reference.
Currently, humeral stem positioning does not provide for recordation of orientation of trials while allowing adjustment of inclination, head diameter, offset, eccentricity and version of the humeral head with respect to the humeral stem in situ.
Methods, devices and instrumentation of this invention seek to allow variable or incremental adjustment of inclination, diameter, offset, eccentricity and version in situ and recordation of these positions utilizing adjustment instrumentation and trials. Variable adjustment of inclination and version is possible without reliance on extensive use of interchangeable components. Accurate recordation of positioning is also possible, so that optimal positioning of the implant may be reproduced.
Methods, devices and instrumentation of this invention seek to provide a modular prosthesis in which a humeral head component, chosen to suit a patient, is attached to a stem chosen to suit the resected humerus of the patient using an intermediate connecting component. A set of prostheses is able to accommodate a wide range of variation, in a relatively inexpensive manner, by providing many of the variations required in the intermediate connecting component rather than in the more expensive humeral head.
Methods, devices and instrumentation of this invention utilize a series of trial intermediate connecting components which may be any one or a combination of offset, eccentric and angled and which mate with eccentric or non-eccentric humeral heads of various diameters and thicknesses. The trial intermediate connecting components and heads include structure corresponding to structure of an adjustment instrument according to this invention, so that the trial intermediate connecting components and heads may be adjusted either as one unit or independently. Adjustments in the inclination, offset, diameter, eccentricity and version of the humeral head is allowed. The design of the trials and instrumentation is such that the inclination, version, diameter, eccentricity and offset may be adjusted in situ. The instrumentation and trials also include features that indicate the relationship between the components, including the relationship between the head and the intermediate connecting component, as well as the relationship between the assembly of the head and intermediate connecting component and the humeral stem.
As used herein, component refers to any of the parts of a humeral prosthesis or trialing system. A modular humeral prosthesis or modular trailing system according to this invention generally comprises a stem to be fitted to a resected humerus, a head sized and configured to approximate the humeral head, and interconnecting component which may, but need not, take the form of an intermediate connecting component for connecting the stem to the head. Such an intermediate connecting component can include a first connector or connecting surface for connecting the intermediate connecting component to the stem, and a second connector or connecting surface for connecting the intermediate connecting component to the head. The first and second connectors on different intermediate connecting components may be disposed at different angles, and they may or may not have offsets relative to each other, in order to allow the surgeon a range of options in orienting the head of the prosthesis relative to the stem and the humerus.
While the surgeon will still need a traditional range of head sizes and stem sizes and lengths, the surgeon does not need additional heads or stems to provide a particular orientation of the head or a particular offset for the head. Thus, although a range of intermediate connecting components are required to be available to choose particular offsets and orientations, those intermediate connecting components are relatively inexpensive and less in number when compared with the high cost of the highly sophisticated head component, and the quantity of humeral heads that are required to provide the same degree of intraoperative flexibility.
In addition, the surgeon is able to choose the component parts independently of one another. Thus, the surgeon does not have to be concerned with questions of offset and orientation when selecting the correct head size and eccentricity. The same is true with regard to the stem, the surgeon can choose the correct stem to fit the medullary canal in the humerus, thus providing a long lasting and secure joint between the stem and the bone. Having selected these components, the surgeon can independently decide on the particular offset and orientation of the head relative to the stem and select an intermediate connecting component accordingly. The surgeon is, therefore, able to match the modular prosthesis used to the original anatomy of a particular patient with respect to the current position and soft tissue structures. Having matched the trialing head and connecting component and having obtained optimal positioning using the adjustment instrument of this invention, the surgeon may then utilize indicia provided to record the desired position, and repeat this positioning in the actual implant.
One feature of this invention is the ability to readjust version, inclination and eccentricity in situ without removal of the head or stem.
Another feature of this invention is the ability to use an adjustment instrument easily to adjust position or orientation of the intermediate connecting component, the humeral head, or both.
Another feature of this invention is the ability to read indicia directly in order to match or replicate the positioning or orientation of the implant exactly to the position of the trial.
Another feature of this invention is readjustment of positioning or orientation without a loosening and tightening of the trial portions and with reference to prior positioning of the trials.
Another feature of this invention is the ability to adjust inclination, version and eccentricity, or any combination thereof, simultaneously without being required to interchange components to adjust each individual aspect of the humeral head position.
These and other features of this invention will become apparent from the drawings and description below.